1. Technical Field
The present invention relates to a piezoelectric device and a method of driving a piezoelectric device.
2. Related Art
A piezoelectric element generally includes a piezoelectric layer having electromechanical conversion properties, and two electrodes through the piezoelectric layer. In recent years, a device using such a piezoelectric element as a driving source (piezoelectric device) has been actively developed. Examples of the piezoelectric device include a liquid ejecting head represented by an ink jet recording head, an MEMS factor represented by a piezoelectric MEMS element, an ultrasonic measuring apparatus represented by an ultrasonic sensor or the like, and a piezoelectric actuator apparatus.
For the piezoelectric layer, piezoelectric materials such as lead zirconate titanate (Pb(Zr,Ti)O3, refer to as “PZT” below) and sodium potassium niobate ((K,Na)NbO3, refer to as “KNN” below) are used. To PZT, which is one of the piezoelectric materials, an excessive amount of lead (Pb) is added in order to secure piezoelectric properties. However, it is known that the excessive amount of Pb degrades voltage withstanding characteristics, and a method of driving a piezoelectric device and the structure of a piezoelectric element are devised to improve the voltage withstanding characteristics of PZT.
For example, JP-A-2013-159081 discloses a method of driving a piezoelectric device in which a driving waveform applied to a first electrode is a waveform in which voltage increases or decreases based on an intermediate voltage, and by applying a reference voltage which is higher than the intermediate voltage to a second electrode, a driving waveform having a relatively low intermediate voltage is applied to an individual electrode in a state in which a relatively high voltage is applied to a common electrode opposite to a pressure generating chamber. In addition, International Publication No. 2005/028207 discloses a piezoelectric element having a structure in which a pattern region of each layer at least configuring the piezoelectric element is covered by an insulating film made of an inorganic insulating material so that deterioration (breakage) of a piezoelectric layer (piezoelectric element) caused by an external environment such as moisture (humidity) is reliably prevented for a long period of time.
Generally, it is known that the voltage withstanding characteristics and the like of a piezoelectric material are degraded due to deterioration over time. However, in JP-A-2013-159081 and International Publication No. 2005/028207, methods for improving the voltage withstanding characteristics of a piezoelectric material are merely disclosed and there is no description of extending the service life by preventing degradation of voltage withstanding characteristics due to deterioration over time.